1. Field of the Invention
The present invention relates to technique used for forming a ball rolling groove in a guide rail material of a linear guide by form rolling.
2. Description of the Related Art
A guide rail of a linear guide is generally produced by a method having the steps of: drawing a guide rail material of iron or steel out so as to be formed into a predetermined shape; and grinding ball rolling grooves formed in surfaces (e.g., side surfaces) of the guide rail material, on a grind stone. To obtain an accurate guide rail by this method, it is however necessary that the machining allowance for grinding the ball rolling grooves is selected to be a little bit great, and the grinding of the ball rolling grooves is repeated. This causes elongation of the machining time and increase in the production cost of the guide rail.
Therefore, a method using a rolling die D as shown in FIG. 11 for forming ball rolling grooves in a guide rail material by form rolling to thereby produce a guide rail disposed in JP-A-2001-227539.
According to the method, the production cost of the guide rail can be reduced because it is unnecessary to repeat grinding of the ball rolling grooves but there is the possibility that the following problem may occur. That is, when the rolling die D shown in FIG. 11 is simply used for forming ball rolling grooves in a guide rail material by form rolling (in the condition that the die (form rolling roll) is not applied to side surfaces of the rail), joint portions (A in FIG. 12) between each ball rolling groove G formed in the guide rail material W by form rolling and a surface of the guide rail material are apt to be swollen like edges, as shown in FIG. 12. For this reason, there is the possibility that a ball may collide with the joint portions when the ball enters a load portion of a slider. Hence, there is fear that stress produced by collision of the ball with the joint portions may be concentrated into the edges of the joint portions to thereby lower durability of the guide rail. There is also fear that abrasion of a side seal mounted on the slider may be accelerated to thereby lower the function of the side seal.